The present invention relates to an ignition control apparatus for an internal combustion engine. More particularly, the invention relates to an electrical ignition control apparatus which has an electrical circuit to which a fixed D.C. voltage should be supplied as a voltage supply.
In electrical ignition control apparatuses for internal combustion engines, a calculation of the ignition timing is performed based on signals indicating conditions of the engine, for example, an air flow signal for indicating a quantity of air sucked into the engine or a vacuum level signal for indicating the vacuum level in an intake manifold of the engine and a rotational speed signal for indicating the rotational speed of the engine. Thereafter, the timing of sparks produced by spark plugs mounted on cylinders of the engine is controlled according to the results of the above-mentioned calculations.
An ignition control apparatus of this type comprises, in general, a digital electronic circuit such as a micro-processor and a digital memory element. In order to actuate and operate this digital electronic circuit, a fixed D.C. voltage supply, for example, a 5-V D.C. supply, is necessarily required. In the case of an automobile internal combustion engine, an automobile battery is ordinarily used as the power supply source for an electronic circuit of this type. The terminal voltage of this automobile battery, however, changes greatly depending on the driving condition of the engine. Especially at the time of starting the engine, a large current flows into a starter motor and variation of the voltage is extreme. When the temperature of the outer atmosphere is low or the battery is degraded, the terminal voltage of the battery is often lower than 5 V at the time of starting the engine.
Accordingly, in a conventional control apparatus of this type, the occurrence of trouble in the above-mentioned electronic circuit at the time of starting the engine or during the driving operation is prevented by elevating the battery voltage by using a D.C. converter, adjusting the elevated voltage to a predetermined fixed voltage and finally supplying the fixed voltage to the electronic circuit. However, since this D.C. converter is very expensive and large in volume, installation of the D.C. converter on an automobile involves problems of cost, space and the like.